Snap acting thermally responsive electrical switch



Feb 1967 L. MARCOUX 3,305,655

SNAP ACTING THERMALLY RESPONSIVE ELECTRICAL SWITCH Filed Feb. 18, 1965 2 Sheets-Sheet 1 United States Patent O 3,305,655 SNAP ACTING THERMALLY RESPONSIVE ELECTRICAL SWITCH Leo Marcoux, Pawtucket, R.I., assignor to Texas Instruments Incorporated, Dallas, Tex., a corporation of Delaware Filed Feb. 18, 1965, Ser. No. 433,677 6 Claims. (Cl. 200-138) This invention relates to thermally responsive electrical switches and in particular to such switches which are especially suited for miniaturized, hermetically sealed constructions.

Among the several objects of this invention may be noted the provision of new and improved thermally responsive electrical switches which permit fast response, and are adapted for miniaturization so as to be conveniently insertable into small spaces adjacent the heated parts to which a temperature response is to be made by the switch; the provision of such switches which are especially adapted for hermetically sealed constructions; the provision of such switches which are precise, accurate, compact and reliable in operation; the provision of such switches which provide for improved vibration and shock resistance and which are relatively insensitive to position orientation; the provision of such switches which embody a minimum number of parts, are relatively simple in construction and are economical to assemble and manufacture, and the provision of a thermostatic miniaturized switch having improved current capacity.

Other objects will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations of elements, features of construction and arrangements of parts which will be exemplified in the structures hereinafter described, and the scope of the application of which will be indicated in the following claims.

In the accompanying drawings, in which several of the various possible embodiments of the invention are illustrated:

FIG. 1 is a plan view of a thermally responsive electrical switch according to the present invention;

FIG. 2 is a plan view of a spring member employed in the switch shown in FIG. 1;

FIG. 3 is an elevational view of the spring member shown in FIG. 2;

FIG. 4 is a sectional view taken on line 44 of FIG. 1, showing the device in the contacts closed position; and

FIG. 5 is a view similar to that of FIG. 4, showing the device in the contacts open position.

Similar reference characters indicate corresponding parts throughout the several views of the drawings. Dimensions of certain of the parts, as shown in the drawings, have been modified for the purpose of clarity of illustration.

Referring now to the drawings, particularly FIGS. 4 and 5, there is shown a switch embodying the invention of this application and generally referred to by reference numeral 10, which takes the form of a hermetically sealed, thermally responsive, snap-acting, electrical switch. Switch includes a housing or sleeve assembly generally indicated by reference numeral 12. Retained within sleeve assembly 12 is a disc and contact assembly 14. A cover assembly 16 closes the switch package 10'.

Housing assembly 12 includes an open-ended, cylindrical, tubular sleeve member 18 formed of a suitable electrically insulating material such as, for example, ceramic. Each end of sleeve 18 includes a circumferentially extending metal layer 20 which is bonded to the ends of sleeve 18. Metal layer 20 is preferably of a type which is easily s-olderable such as, for example, a molybdenum manganese alloy. Disposed on one end of the sleeve 18 and soldered or brazed to the surface 20 is an end or base plate member 22 formed of a suitable, electrically and thermally conductive material such as, for example, brass or cold rolled steel. As best seen in FIG. 1, base plate 22 includes a tab portion 24 to which may be welded an electrically conductive lead 26.

On the other end of tubular sleeve 18 from base plate 22 there is attached by soldering or brazing to metal surface 20, a circumferentially extending flange 28. This structure completes the housing subassembly 12.

Disc assembly 14 is enclosed within housing assembly 12 by cover assembly 16 which includes a cap or cover plate 30 formed of a suitable electrically and thermally conductive material such as that used to form base plate 22. Cover plate 30 is resistance brazed or welded to flange 255 on the interior side of cover 30. On the same interior side of cover 30, in a central portion thereof, is welded a con-tact member 32 in electrically conductive relationship with cover 30. As best seen in FIG. 1, cover assembly 16 also includes a tab portion 34 extending from cover 30 to which may be welded a lead 36 similar to lead 26 and tab 24. Cover 30 is deformed to provide a circumferentially extending abutment or shoulder 38 which permits calibration of the switch 10 and inhibits creep action as will be described further in the description. Abutment 38 also provides a self locating mechanism for ease of locating the cover 30 in cover assembly 16 in sleeve assembly 12 during the assembly of switch 10.

Retained within housing assembly 12 is the disc assembly 14 which includes a snap acting, composite, thermostatic disc type element 40 which is deformed along at least a portion of its extent in order to provide it with snap action response to temperature change.

As best seen in FIG. 5, disc 40 includes a central aperture 42 on which is mounted a bushing 45 formed of a suitable electrically insulating material such as, for ex ample, a ceramic. Located in loose fitting relationship within aperture 42 of disc 40 is the shank portion 44 of bushing 45. A head portion 46 of bushing 45 is of greater diameter than shank 44 and aperture 42 and thus provides a shoulder which retains the shank portion 44 within aperture 42 of disc 40 and which restricts the movement of disc 40 relative to shank 44 in one direction.

Located on the other end of shank 44 from shoulder 46 is a shield plate formed of a suitable electrical insulating material such as ceramic. Abutting shield plate 48 and located on the side of the disc assembly 14 facing stationary contact 32 and in registry therewith is a movable electrical contact 50. As seen in the drawing,

FIGS. 4 and 5, ceramic shield plate 48 has a diameter substantially larger than the dimensions of either of contact 32 or contact 50 and because of its location between those contacts and the disc 40, it advantageously pro vides an arc shield for the disc 40 thus protecting its calibration and temperature setting. In addition, plate 48 limits the movement of disc 40 relative to bushing shank 44 in the direction opposite to that limited by shoulder 46.

Located on the opposite side of disc assembly 14 from the cover assembly 16 and on the side facing base plate 22 is a spring member 54 formed of a suitable spring material having good electrical and thermally conductive properties such as, for example, beryllium copper. As best seen in FIGS. 2 and 3, spring member 54 is generally circular in form and has a diameter which closely approximates that of the interior diameter of sleeve 18. Spring 54 includes a plurality of spring fingers 56 which fingers are struck out of and bent from the plane of spring 54.

In generally planar central portion 55 spring 54 is located an aperture 58. The struck out spirng fingers 56 rest on the peripheral portions of base plate 22 while the 3 planar aperture portion 55 of spring 54 rests against the head portion 46 of the bushing 45. Centrally located aperture 58 is in registry with apertures 60 and 62 located centrally in shank 44 of bushing 45 and plate 42 respectively.

Attached in electrically conductive relationship with or formed integrally on contact 50 is a shank member 52. Shank member 52 extends through apertures 62, 60 and 58 and is struck over at 53 to retain contact 50, plate or shield 48, bushing 45, and spring 54 in unitary static relationship. This structure, together with loosely held disc 40 forms the disc assembly 14.

It will be seen that spring 54 urges the disc assembly 14 in a direction towards cover assembly 16. Creep action of disc 14 resulting in creeping Open and creeping closing of the contacts 32 and 50 is advantageously prevented by the construction of this device. As best seen in FIG. 4, in the contacts closed position, disc 46 is free of abutment 38 and the contacts 32 and are held in engagement by the force of spring 54 which bias the disc assembly and contact 50 into engagement with contact 32. In this position, disc 40 is free to experience some creep action without contacts 32 and 50 opening and until the snap range of the disc is achieved. Thus, the disc 40 can creep until it arrives at its snap range and when this range is achieved, contacts 32 and 50 snap open. Further, since the contacts are retained in engagement by spring 54, the contact chatter as a result of vibra tion is substantially reduced.

Conversely when the disc is in the contacts open position shown in FIG. 5, the peripheral portion of disc 40 is in engagement with abutment 38 and is biased into engagement by the spring 54. As disc 40 experiences a temperature change and creeps toward the contacts closed position shown in FIG. 4, contact 50 does not engage contact 32 until the disc 40 reaches its snap range and contact 50 is snapped into engagement with contact 32. There is substantially no creeping actuation or deactuation of the contacts.

A further advantage of the instant construction is that since abutment 38 is an integral portion of the cover assembly, the device may be calibrated by a simple metals forming operation which can be precisely controlled. This calibration is achieved by adjusting the height of the stationary contact relative to the abutment as a function of the disc snap characteristics.

The electrical path of the device is as follows: from lead 36 to tab 34 on cover plate 30 to contact 32, contact 50, contact shank 52, spring 54 through spring fingers 56 to end plate 22 and its tab 24 and out through to lead 26. It will thus be seen that although the disc 40 is not electrically isolated, it does not carry current and thus for the same disc configuration current heating of the disc is substantially reduced, thus increasing the current carrying capacity of the device.

Further, since the disc 40 is spring loaded at its center rather than at its periphery, the spring loading is uniformly distributed and the disc does not experience the nonuniform distribution of force that would be experienced were the force exerted on the periphery at the disc.

It will be seen that the co-operation between the disc 40, abutment 38 and spring 54 advantageously provides for improved vibration and shock resistance of the switch 10.

Further, this co-operation provides a substantial contact opening gap when the disc is in the contact open position as shown in FIG. 4 to inhibit vibration induced closing of the contacts. Further, this cooperation'serves to maintain desired contact pressure between the contacts 32 and 50 in the contacts closed FIG. 5 position. Further, the spring provides good electrical conductivity between the plate 22 and the electrically conductive shank 52.

It will be seen that the instant invention avoids the necessity for fixedly securing the disc to any supporting means. This is particularly significant in miniature devices. It will be understood that other forms of springs than that shown in FIGS. 2 and 3 may be employed so long as the disc is spring biased at its center.

In view of the above it will be seen that the several objects of the invention are achieved and other advantageous results attained.

It is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practised or carried out in various ways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

As many changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense, and it is also intended that the appended claims shall cover all such equivalent variations as come within the true spirit and scope of the invention.

1 claim:

1. A thermally responsive electrical switch comprising, in combination:

(a) an open-ended tubular sleeve formed of an electrically insulating material;

(b) a plate member having an electrically conductive portion and secured to and closing one end of the sleeve;

(0) a cap member having an electrically conductive portion and secured to and closing the other end of the sleeve;

(d) a stationary electrically conductive contact mounted on and electrically connected to the electrically conductive portion of the cap member;

(e) a composite, thermally responsive, snap-acting element disposed within the sleeve;

(f an aperture formed in a central portion of the snapacting element;

(g) an electrically insulating bushing mounted in the aperture in the snap acting element, the electrically insulating bushing including a shank portion retained in loose fitting relation in the aperture and a head portion on one end of the shank which provides a shoulder to limit the movement of the thermally responsive element with respect to the shank in a first direction,

(h) a movable electrically conductive contact member mounted on the bushing and located for movement into and out of engagement with the stationary contact in response to snap movement of the thermally responsive element;

(i) an electrically conductive plate located between the other end of the bushing shank and the movable contact member, the plate having a diameter greater than the movable contact and the bushing shankwhereby the movement of the thermally responsive element in a direction opposite to the first direction along the bushing shank is limited and whereby an arc shield is provided between the contacts and the thermally responsive elements;

(j) an annular abutment portion formed on the cap member and positioned in the sleeve intermediate the thermally responsive element and the contact memher for engagement with a portion of the element, the abutment portion engaging peripheral portions of the thermally responsive element when the contacts are out of engagement to permit the thermally responsive element to move with creep movement without permitting the contacts to become engaged, the abutment portion being located out of engagement with the peripheral portions of the thermally responsive member when the contacts are in engagement to permit the thermally responsive element to move with creep movement without its engaging the contacts;

(k) electrically conductive spring means disposed in the sleeve in electrically conductive relationship with the electrically conductive portion of the plate member and a portion of the movable contact thereby establishing an electrically conductive path therebetween, the spring means comprising a member formed of thermally and electrically conductive material having a diameter closely approximating that of the tubular sleeve and including a plurality of spring fingers bent out of the plane of the spring member to engage the plate member in electrically conductive relationship at spaced portions adjacent the periphery of the plate member, the central portion of the spring means abutting the head portion of the bushing, the spring means urging the thermally responsive element for movement away from the plate member and toward the abutment member and stationary contact;

(1) the plate, shield, bushing and spring each having apertures formed in central portions thereof and the plate, shield, bushing and spring being located such that their apertures are in registry and, the contact element including a shank member located within the apertures, one end of the contact shank mounting the movable contact in electrically conductive relation and the other end being headed over to engage the spring member in electrically conductive relation whereby the plate, shield, bushing and spring are retained in unitary static relationship.

2. A thermally responsive electrical switch comprising,

in combination:

(a) an open-ended tubular sleeve formed of an electrically insulating material;

(b) a plate member having an electrically conductive portion and secured to and closing one end of the sleeve;

(c) a cap member having an electrically conductive portion and secured to and closing the other end of the sleeve;

(d) a stationary electrically conductive contact mounted on and electrically connected to the electrically conductive portion of the cap member;

(e) a composite, thermally responsive, snap-acting element disposed within the sleeve;

(f) an aperture formed in a central portion of the snapacting element;

(g) an electrically insulating bushing mounted in the aperture in the snap acting element, the electrically insulating bushing including a shank portion retained in loose fitting relation in the aperture and a head portion on one end of the shank which provides a shoulder to limit the movement of the thermally responsive element with respect to the shank in a first direction;

(h) a movable electrically conductive contact member mounted 011 the bushing and located for movement into and out of engagement with the stationary contact in response to snap movement of the thermally responsive element;

(i) an annular abutment portion formed on the cap member and positioned in the sleeve intermediate the thermally responsive element and the contact member for engagement with a portion of the element;

(j) electrically conductive spring means disposed in the sleeve in electrically conductive relationship with the electrically conductive portion of the plate memher and a portion of the movable contact thereby establishing an electrically conductive path therebetween, the spring means urging the thermally responsive element for movement away from the plate member and toward the abutment member and stationary contact.

3. A switch as set forth in claim 2 wherein the device includes an electrically conductive plate located between the other end of the bushing shank and the movable contact member, the plate having a diameter greater than that of the movable contact and the bushing shank whereby the movement of the thermally responsive element in a direction opposite to the first direction along the bushing shank is limited and whereby an arc shield is provided between the contacts and the thermally responsive element.

4. A switch as set forth in claim 3 wherein the plate, shield, bushing and spring each have apertures formed in central portions thereof and wherein the plate, shield, bushing and spring are located such that their apertures are in registry and wherein the contact element includes a shank member located within the apertures and wherein one end of the contact shank mounts the movable contact in electrically conductive relation and the other end is headed over to engage the spring member in electrically conductive relation, and whereby the plate, shield, bushing and spring are retained in unitary static relationship.

5. A switch as set forth in claim 2 wherein the spring means comprises a member formed of thermally and electrically conductive material having a diameter closely approximating that of the tubular sleeve and includes a plurality of spring fingers bent out of the plane of the spring member to engage the plate member in electrically conductive relationship at spaced portions adjacent the periphery of the plate member and wherein the central portion of the spring abuts the head portion of the bushing.

6. The switch as set forth in claim 2 wherein the abutment portion engages peripheral portions of the thermally responsive element when the contacts are out of engagement to permit the thermally responsive member to move with creep movement without permitting the contacts to become engaged and wherein the abutment portion is located out of engagement with the peripheral portions of the thermally responsive member when the contacts are in engagement to permit the thermally responsive element to move with creep movement without its engaging the contacts.

References Cited by the Examiner UNITED STATES PATENTS 3,091,121 5/1963 Moorhead 200138X 3,213,250 10/1965 MarcouX 200138 BERNARD A. GILHEANY, Primary Examiner. T. MACBLAIN, H. A. LEWITTER, Assistant Examiners. 

1. A THERMALLY RESPONSIVE ELECTRICAL SWITCH COMPRISING, IN COMBINATION: (A) AN OPEN-ENDED TUBULAR SLEEVE FORMED OF AN ELECTRICALLY INSULATING MATERIAL; (B) A PLATE MEMBER HAVING AN ELECTRICALLY CONDUCTIVE PORTION AND SECURED TO AND CLOSING ONE END OF THE SLEEVE; (C) A CAP MEMBER HAVING AN ELECTRICALLY CONDUCTIVE PORTION AND SECURED TO AND CLOSING THE OTHER END OF THE SLEEVE; (D) A STATIONARY ELECTRICALLY CONDUCTIVE CONTACT MOUNTED ON AND ELECTRICALLY CONNECTED TO THE ELECTRICALLY CONDUCTIVE PORTION OF THE CAP MEMBER; (E) A COMPOSITE, THERMALLY RESPONSIVE, SNAP-ACTING ELEMENT DISPOSED WITHIN THE SLEEVE; (F) AN APERTURE FORMED IN A CENTRAL PORTION OF THE SNAPACTING ELEMENT; (G) AN ELECTRICALLY INSULATING BUSHING MOUNTED IN THE APERTURE IN THE SNAP ACTING ELEMENT, THE ELECTRICALLY INSULATING BUSHING INCLUDING A SHANK PORTION RETAINED IN LOOSE FITTING RELATION IN THE APERTURE AND A HEAD PORTION ON ONE END OF THE SHANK WHICH PROVIDES A SHOULDER TO LIMIT THE MOVEMENT OF THE THERMALLY RESPONSIVE ELEMENT WITH RESPECT TO THE SHANK IN A FIRST DIRECTION, (H) A MOVABLE ELECTRICALLY CONDUCTIVE CONTACT MEMBER MOUNTED ON THE BUSHING AND LOCATED FOR MOVEMENT INTO AND OUT OF ENGAGEMENT WITH THE STATIONARY CONTACT IN RESPONSE TO SNAP MOVEMENT OF THE THERMALLY RESPONSIVE ELEMENT; (I) AN ELECTRICALLY CONDUCTIVE PLATE LOCATED BETWEEN THE OTHER END OF THE BUSHING SHANK AND THE MOVABLE CONTACT MEMBER, THE PLATE HAVING A DIAMETER GREATER THAN THE MOVABLE CONTACT AND THE BUSHING SHANK WHEREBY THE MOVEMENT OF THE THERMALLY RESPONSIVE ELEMENT IN A DIRECTION OPPOSITE TO THE FIRST DIRECTION ALONG THE BUSHING SHANK IS LIMITED AND WHEREBY AN ARC SHIELD IS PROVIDED BETWEEN THE CONTACTS AND THE THERMALLY RESPONSIVE ELEMENTS; (J) AN ANNULAR ABUTMENT PORTION FORMED ON THE CAP MEMBER AND POSITIONED IN THE SLEEVE INTERMEDIATE THE THERMALLY RESPONSIVE ELEMENT AND THE CONTACT MEMBER FOR ENGAGEMENT WITH A PORTION OF THE ELEMENT, THE ABUTMENT PORTION ENGAGING PERIPHERAL PORTIONS OF THE THERMALLY RESPONSIVE ELEMENT WHEN THE CONTACTS ARE OUT OF ENGAGEMENT TO PERMIT THE THERMALLY RESPONSIVE ELEMENT TO MOVE WITH CREEP MOVEMENT WITHOUT PERMITTING THE CONTACTS TO BECOME ENGAGED, THE ABUTMENT PORTION BEING LOCATED OUT OF ENGAGEMENT WITH THE PERIPHERAL PORTIONS OF THE THERMALLY RESPONSIVE MEMBER WHEN THE CONTACTS ARE IN ENGAGEMENT TO PERMIT THE THERMALLY RESPONSIVE ELEMENT TO MOVE WITH CREEP MOVEMENT WITHOUT ITS ENGAGING THE CONTACTS; (K) ELECTRICALLY CONDUCTIVE SPRING MEANS DISPOSED IN THE SLEEVE IN ELECTRICALLY CONDUCTIVE RELATIONSHIP WITH THE ELECTRICALLY CONDUCTIVE PORTION OF THE PLATE MEMBER AND A PORTION OF THE MOVABLE CONTACT THEREBY ESTABLISHING AN ELECTRICALLY CONDUCTIVE PATH THEREBETWEEN, THE SPRING MEANS COMPRISING A MEMBER FORMED OF THERMALLY AND ELECTRICALLY CONDUCTIVE MATERIAL HAVING A DIAMETER CLOSELY APPROXIMATING THAT OF THE TUBULAR SLEEVE AND INCLUDING A PLURALITY OF SPRING FINGERS BENT OUT OF THE PLANE OF THE SPRING MEMBER TO ENGAGE THE PLATE MEMBER IN ELECTRICALLY CONDUCTIVE RELATIONSHIP AT SPACED PORTIONS ADJACENT THE PERIPHERY OF THE PLATE MEMBER, THE CENTRAL PORTION OF THE SPRING MEANS ABUTTING THE HEAD PORTION OF THE BUSHING, THE SPRING MEANS URGING THE THERMALLY RESPONSIVE ELEMENT FOR MOVEMENT AWAY FROM THE PLATE MEMBER AND TOWARD THE ABUTMENT MEMBER AND STATIONARY CONTACT; (L) THE PLATE, SHIELD, BUSHING AND SPRING EACH HAVING APERTURES FORMED IN CENTRAL PORTIONS THEREOF AND THE PLATE, SHIELD, BUSHING AND SPRING BEING LOCATED SUCH THAT THEIR APERTURES ARE IN REGISTRY AND, THE CONTACT ELEMENT INCLUDING A SHANK MEMBER LOCATED WITHIN THE APERTURES, ONE END OF THE CONTACT SHANK MOUNTING THE MOVABLE CONTACT IN ELECTRICALLY CONDUCTIVE RELATION AND THE OTHER END BEING HEADED OVER TO ENGAGE THE SPRING MEMBER IN ELECTRICALLY CONDUCTIVE RELATION WHEREBY THE PLATE, SHIELD, BUSHING AND SPRING ARE RETAINED IN UNITARY STATIC RELATIONSHIP. 